
The Tensile Strengths of the 
Copper-Zinc Alloys 



A THE5I5 

PRESENTED TO THE FACULTY OF THE GRADUATE 

SCHOOL OF CORNELL UNIVERSITY FOR THE 

DEGREE OF DOCTOR OF PHILOSOPHY 



By JAML5 MARTIN LOHR 



Reprinted from the Journal of Physical Chemistry, Vol. XVII, No. 1. Jan., 1913. 



The Tensile Strengths of the 
Copper-Zinc Alloys 



A THL515 



PRESENTED TO THE FACULTY OF THE GRADUATE 

SCHOOL OF CORNELL UNIVERSITY FOR THE 

DEGREE OF DOCTOR OF PHILOSOPHY 



By JAML5 MARTIN LOHR 



Reprinted from the Journal of Physical Chemistry, Vol. XVII, No. 1, Jan., 1913. 






/-^ 



THE TENSILE STRENGTH OF THE COPPER-ZINC 

ALLOYS^ 



BY J. M. LOHR 

The following investigation was undertaken for the 
purpose of establishing the relationship between the consti- 
tution of the copper-zinc alloys and their tensile strengths. 
For a long time such a series of data has been badly needed. 
Although brass has been used commercially for many years, 
it was only eight years ago that the equilibrium diagram w^as 
worked out, and it is not strange that, prior to that time, 
investigations on the various physical properties were made 
largely without any scientific basis as a guide for the work 
and for the interpretation of the results. 

As early as 1842, Mallet^ reported upon the specific 
gravities, color and character of fracture, tensile strengths, 
order of ductility, order of malleability, order of hardness 
and order of fusibility of the brasses. He used twenty- three 
pieces to cover the w^liole series, while only eleven of these 
covered the useful alloys. These alloys contained from about 
47 to 100 percent copper, which are the percentages used in 
this work. 

However, the most comprehensive work on this subject 
was that of the United States Board for Testing Materials, 
conducted by the Committee on Alloys under the chairman- 
ship of Dr. R. H. Thurston.^ This work was very extensive, 
and hence no part of it could be studied in detail. Forty- two 
pieces were used in the series of tests, twenty- three of which 
cover the useful part of the series. 

More recently, important researches have been made on 
the effects of heat treatment, the principal ones of which 



^ A paper read before the Eighth International Congress of Applied 
Chemistry in New York, September, 19 12. 
-Phil. Mag., [3] 21, 66 (1842). 
^ Thurston: Materials of Engineering, Part 3. 



2 /. M. Lohr 

are by Charpy/ Girard/ Cubillo,^ and Bengough and Hudson/ 
In most cases, these have been intensive studies of alloys with 
definite compositions, rather than upon a series of different 
compositions. 

The Equilibrium Diag-ram 
In Fig. I, the equilibrium diagram for the copper-zinc 
series is shown, as worked out by Shepherd,^ and recently 
very slightly modified by Carpenter and Edwards.^ The 
coordinates are temperatures and percentage composition. 
The various lines on the diagram show where certain chemical 
or physical changes take place. The upper heavy lines, or 




Fig. I 

liquid us, represent the temperatures above which the alloys 
are completely melted. The dotted lines or solidus, just below, 

} Bulletin de la Societe d' Encouragement de I'Etude des Alliages, page i. 
^ Revue de Metallurgie, 1909; Memoires, page 1069. 
^ Proc. Inst. Mech. Eng., 791 (1905). 

* Jour. Soc. Chem. Ind., 27, 43, 654 (1908); Engineering, 90, 447 (1910). 
^ Jour. Phys. Chem., 8, 421 (1904). 

''Engineering, 91, 200 (1911); 92, 431 (1912); Jour. Inst. Metals, 7, 70 
(1912). 



Tensile Strengths of Copper-Zinc Alloys 3 

show the limits below which the alloys are completely solid. 
Between these lines crystals and melt co-exist. 

In the diagram, the field marked a shows the concentra- 
tion and temperatures over which pure crystals are stable under 
equilibrium conditions. These crystals are composed of a 
solid solution of zinc in copper, and show the same fern leaf- 
like structure throughout. Likewise, /?, j, d, £, and 7) show 
definite crystal forms in their respective fields as indicated. 
Also, as we pass from a to /? we find a field 5^, b^, b^, b^, which is 
not composed of pure a or pure ^ crystals, but is a mixture 
of these two, which is richer in a crystals on the side bordering 
on pure a, and richer in /? as we approach the field of pure /?. 
Similarly we find fields composed oi a + y, /^ + y, y + e, 
d + £ and e -\- r). 

Let us now trace the chemical changes which occur in 
the cooling of an alloy of a given composition. An alloy 
of, for example, 55 percent copper, is in the molten condition 
somewhere above 880°, the temperature at which it begins to 
solidify. Between this temperature and that represented by 
the dotted line, which is about 860°, /? crystals begin to separate 
from the mother liquor. These continue to separate as the 
temperature drops. When the dotted line, or solidus, is 
reached the melt freezes completely, and the mass is composed 
of pure /5 crystals. As the mass continues to cool, /? crystals 
begin to break down into a crystals. This change begins 
at about 600°. As the cooling progresses, more and more 
/? crystals break down into a crystals. Thus we have a mix- 
ture of a + ^ crystals, until we reach a temperature of 470°, 
at which point the ,5 crystals break down into y crystals. 
Below this temperature we find a mixture of a +;- crystals. 
This condition results from very slow cooling. If, however, 
we take the same 55 percent alloy, cool slowly, and then heat 
it to some high temperature, somewhere below the initial 
freezing point, for example 800°, and hold it there until 
equilibrium conditions are attained, it will be composed of 
pure /? crystals. If quenched quickly in water from this 



4 J- M. Lohr 

temperature, the ;3 crystals do not have time to change over 
into a crystals, and at ordinary temperatures the alloy retains 
the same crystalline structure which it had at 800°. One 
could, therefore, determine the strength of a pure ,5 alloy by 
annealing a 55 percent alloy at 800°, or any other tempera- 
ture falling within the ,5 field, until equilibrium is reached, 
and then quench it rapidly; or, what is equivalent, if we quench 
the bar immediately after casting, we attain practically the 
same results. 

As the alloys containing less than 50 percent copper are 
extremely brittle, and not used very extensively in technical 
work, this report covers only the a,a-\- /?,,5 and a very small 
portion of the ,5 + y fields, a -\- j- does not enter into it as 
all quenching was done considerably above 470° — the upper 
hmit of this field. 

Materials and Apparatus 

The crucibles used in this work were made from cylinders 
of Acheson graphite. Three sizes, measuring respectively, 
4, 6, and 8 inches in diameter and 6, 8, and 10 inches in height 
(outside dimensions), were employed. The smallest crucible 
contained the melt and was placed inside the one of medium 
size; the reason for this will be given later. These crucibles 
were turned from the cylinders by placing them in a lathe 
and using ordinary machine tools. It must be noted, however, 
in passing, that graphite dulls the edges of tools very quickly, 
making it almost impossible to keep tools sharp. But this is 
not a serious handicap as the material cuts easily. These 
graphite crucibles were entirely satisfactory in every respect 
except durability. It was impossible to prevent the heat 
from burning away the surface of the crucibles. In most 
cases about twenty-five pourings were made from a single 
crucible, although in the lower melting alloys many more 
were made. Dixon crucibles were also tried but they proved 
unsatisfactory for this work, chiefly because they chipped 
easily, and furthermore they could not be adapted to the 
method of pouring employed here. 



Tensile Strengths of Copper-Zinc Alloys 5 

About 1600 grams of metal were used for one pouring. 
Experiments were made with amounts varying from 1500 to 
2000 grams, but no advantage seemed to be gained by using 
more than 1600 grams. 

The heating was done in a 30 k. w. electric resistance 
furnace. It was 34 X 23 X 15 inches and was built of 
Queen's Run fire brick and cement. The walls were 4 inches 
thick — the width of a brick. The electrodes were made of 
Acheson graphite 2X4 inches (made up of two 2X2 inches) 
and extended inward through the ends of the furnace about 
7 inches, with 4 inches outside the furnace walls. These 
electrodes were held in place by water-cooled electrode holders/ 
Fig. 2 shows a top view of the furnace. A is the brick wall, 
B a thick lining of siloxicon to prevent loss of heat by radia- 
tion, D the space occupied by granular carbon, C crucibles, 
E electrodes, and F electrode holders. A layer of siloxicon 
about an inch thick was also placed above and below the granu- 
lar carbon. 




fl 



>= 



■^ 



Fisf. 



The outer crucible (the medium size mentioned above) 
was kept stationary in the furnace, with its top very nearly 
on a level with the upper layer of siloxicon, so as to prevent 



Gillett: Jour. Phys. Chem., 15, 213 (191 1) 



6 /. M. Lohr 

burning away as much as possible. The smaller crucible 
containing the charge rested in this one, being on a level with 
the top. A small piece was cut from the inner edge of the 
outer crucible, to admit taking hold of the inner one with 
tongs. By this arrangement the crucible containing the charge 
could be removed at will, without tearing out the furnace 
charge. 

The heating was usually begun with about 125 volts 
across the terminals; as the temperature rose the resistance 
decreased, and the voltage dropped to about 50 volts where it 
was held throughout the greater part of the run. This furnace 
could easily attain a temperature of 1200°, which was ample 
for this work. 

The moulds^ were made of two slabs of Acheson graphite, 
each I X 5 X 17 inches. The pattern of the casting con- 
sisted of the centrifugal sprew, V, inch in diameter, the test- 
piece ten inches in length, and the riser i y^ inches in diameter. 
The test-pieces were cast to size for testing, and were com- 
posed of the test section 0.40 inch in diameter and six inches 
in length, and the grips at the ends 0.75 inch in diameter. 

When casting test-pieces to size, the size of the riser is 
very important. If too small, an insufficient amount of metal 
IS carried beyond the test-piece proper, and consequently any 
slag or oxide carried along in the pouring may lodge in the 
test-piece and render it faulty. 

The moulds were made as needed. A mould could be 
used for about seventy-five castings. The greatest wear 
upon the moulds resulted from the effect of heating, which 
gradually burned away the outside, especially the bottom 
causing the metal to run through when poured into the mould' 
In the preparation of the moulds, the graphite slabs were 
first made smooth on one side by means of a planer or shaper, 
so as to enable them to be clamped tightly together. This 
planing is usually necessary, as the slabs are generally some- 
wha^^warped^en received from the factory. Most of the 

' Shepherd and Upton: Jour. Phys. Chem., 9, 441 (1905). 



Tensile Strengths of Copper-Zinc Alloys 7 

cutting was done by means of ordinary carpenter's gouges, 
but care had to be taken in making the grooves for the test 
section. After cutting out the grooves roughly, the smooth 
inside finish was most satisfactorily produced by means either 
of discarded safety razor blades rounded on end and made 
into scrapers, or short pieces of glass tubing of the proper 
diameter with sharp ends. 

Probably the greatest difficulty encountered in this work 
was that of pouring. The mould was first placed in a level 
position, but it was impossible to fill the test-piece portion 
at the far end. This was due to the hot metal freezing too 
quickly in the bottom portion of the test-piece, and thereby 
leaving unfilled gaps on top. It was noticed, however, that 
the metal in the riser was always homogeneous and of good 
quality. This was, of course, filled from the bottom. Hence 
it seems wise to raise the far end of the mould so that the part 
occupied by the test-piece would fill by being pushed up the 
incline by the weight of the metal. This was an improvement, 
but it was finally found that it could only be filled satisfac- 
torily by both inclining and heating the mould. A large 
box was therefore placed near the furnace and through the 
top of this were projected three gas muffle burners, about 
six inches apart. The box was covered with several sheets 
of asbestos. The mould, clamped tightly together was set 
on blocks of graphite directly over the burners and surrounded 
by fire bricks and sheets of asbestos. The whole apparatus 
was tilted so that the mould was about ten degrees from the 
horizontal (see Fig. 3). The mould was heated to bright 
redness for the higher melting alloys while a dull red was 
sufficient for those melting at lower temperatures. 

As is well known, one of the greatest difficulties in the 
melting of brass is the loss of zinc by oxidation. This oxida- 
tion was cut down by the use of powdered charcoal, sodium 
chloride,^ and by passing illuminating gas directly into the 
crucible, through an iron cover placed over it. These pre- 



^ The Brass World, Sept., 1912, page 307. 



8 /. M. Lohr 

cautions were sufficient to reduce the oxidation of the zinc 
to a minimum, while being heated in the furnace, but the 
moment the crucible was uncovered for pouring, considerable 
oxidation occurred even before the melt could be transferred 
to the mould. In spite of the rapidity of pouring and the use 
of the centrifugal sprew, it was found that when the metal was 
poured from the top of the crucible small pieces of oxide were 
carried into the test section; and, being insoluble in the melt, 
they rendered the casting worthless. This difficulty was 
overcome by pouring from the bottom of the crucible, as in 
the Thermit process, thus avoiding the oxides almost entirely. 
A hole ^/g inch in diameter was bored in the bottom of the 
crucible and close to the inner edge. A graphite plug extend- 
ing to the top of the crucible was fitted into the hole. A 
heavy arm of wood 2X3 inches X 4 feet was screwed in a 
slightly slanting position to a nearby permanent support, 
(see Fig. 3) so as to extend just over the mouth of the mould, 
and a few inches above it. On the end of this arm was screwed 
a heavy iron plate, semi-circular in form with the lower edge 
projecting inward. The crucible could thus be taken from 
the furnace and held by means of tongs on this semi-circular 
support. By means of a previously made gauge- mark on 
the outside of crucible, the hole in the bottom could easily 
be placed directly over the mouth of the mould. While 
holding it in this position the plug could be pulled from the 
top, thereby allowing the metal to be poured in a continuous 
stream. Without this support the drawing of the plug 
usually jarred the crucible so much that a continuous stream 
could not be sent into the mould, without which it is almost 
impossible to get good castings with the type of mould used 
here. In order that the mould, after having been removed, 
could be placed in the proper position with respect to the cru- 
cible, two adjustable iron guards were fastened to the arm just 
back of the semi-circular support. One of these was arranged 
so as to press against the end of the mould and the other 
against the side. By placing the mouth of the mould directly 



Tensile Strengths of Copper-Zinc Alloys 9 

under the outlet of the crucible and adjusting the two guards, 
the mould could be removed and always replaced in the same 
position with respect to the crucible. However, by this method 
of pouring, the excess metal could not be retained in the 
crucible. So an asbestos trough was placed under the front 
end of the crucible and when the mould was filled, the re- 
maining metal was carried into a tank of water. After each 
pouring, the zinc oxide formed during the pouring was scraped 
from the inside of the crucible before placing another charge 
in it. 

Fig. 3 shows the general arrangement of the apparatus. 
A is the mould resting upon graphite blocks and held in place 
by the movable guards E and F. A section of the crucible 



Top Line of Furnace 




Fig- 3 

B, is shown with the hole for pouring and the plug directly 
over the mouth of the mould. C is the frame holding the 
muffle burners. 

After the pouring, the mould was opened quickly and 
the casting immediately quenched in water. As most of 
the castings were quenched from red heat, it was necessary 
to guard against bending the test-piece while removing it 
from the mould, especially as the metal forming the sprew 
and riser was very much heavier than the rod itself, Hence, 
for quenching, a slab of graphite to which was fastened a 



lO /. M. Lohr 

stationary upright strip of iron, was placed across the top 
of the can of water. One-half of the mould was removed, 
and the half containing the casting was placed in an almost 
vertical position on this graphite slab, being supported against 
the iron strip. Then by means of a suitable hook, the casting 
could be removed from the mould and lowered vertically into 
the water. 

The materials used for making the test-pieces were 
electrolytic copper of 99.98 percent pmrity and ptue Bertha 
spelter, thus avoiding the influence of even minute quantities 
of foreign metals. The copper which is sold in twenty-pound 
pigs, was sawed into two pieces and these pieces were melted 
in the electric furnace and recast into small ingots, or granu- 
lated by pouring into water. For this melting the largest of 
the crucibles previously described was packed in the furnace 
and the one of medium size used for the melting. The zinc, 
which is sold in slabs, was broken into small pieces. To avoid 
loss of zinc by volatilization in the subsequent work, at the 
beginning of this set of experiments a large quantity of 50 : 50 
brass was made as a basis for starting. To this, copper could 
then be added to make any desired composition.^ The excess 
metal from pouring and the broken test-pieces were melted 
over and over. In every case, in which pure copper was used, 
it was melted first and then the lower melting alloy, or zinc, 
was added. 

A careful study of the pouring temperatures was made. 
A base metal thermocouple supplied by The Hoskins Manu- 
facturing Company of Detroit, was used for these measure- 
ments. This couple may be placed directly in the melt. 
It was rather satisfactory, but cannot be considered an entire 
success. After using it eight or ten times it would generally 
break, because of corrosion, just back of the twisted ends. 
As nearly as could be ascertained, this corrosion occurred at 
that part of the couple which was at the surface of the melt 
or above it, rather than at the part in the melt. The temper a- 



^ Desch: Metallography, page io8. 



Tensile Strengths of Copper-Zinc Alloys ir 

tures were taken just as soon as the metal reached the molten 
state, and pouring was usually done very soon after this to 
avoid overheating by holding the metal too long in the furnace. 

Testing- 
All of the tests were made on a 10,000-pound Olsen hand 
machine. 

After sawing the metal formed by the sprew and the 
riser from the test-piece, it was tested as cast, except that 
the small fins formed along the test rod by the burning out 
of the graphite around the casting were filed away and the 
center of the piece was filed very slightly, to ensure the locality 
of the break. 

The diameters of the test-pieces were taken at the slightly 
reduced areas by means of a micrometer caliper reading to 
thousandths of an inch. As the pieces were not perfectly 
circular three diameters were taken, and the average used for 
computing the strengths. The records of elongation were 
taken between five-inch lengths on the test-piece, by means 
of fine-pointed dividers, and read on a steel scale divided into 
hundredths of an inch. 

The broken pieces were always examined carefully, 
and the general appearance, together with the character 
of the fracture, as seen under a hand lens, was carefully 
recorded. Much valuable knowledge of the interior of the 
pieces was thus gained. In addition, three diameters of the 
fractured ends were taken, from the average of which, were 
computed tensile strengths, based on the reduced areas. 
Of course, the values thus obtained are not perfectly accurate 
owing to the difficulty of taking accurate measurements on 
such broken ends. But, allowing for the error, they give us 
some interesting data. 

In determining the value of a piece, after making the test, 
it was considered good if it had the proper color and homo- 
geneity, and contained no large holes. It was called good even 
if it contained one or two pinholes of occluded gas. 

On account of the heavy loss of zinc by volatilization 



12 /. M. Lohr 

during the melting, it was impossible to prepare test-pieces 
of a given composition. This could be done to within i per- 
cent in the compositions above 65-70 percent copper, but in 
those of a higher zinc content, it was difficult to come quite 
as close. As a result, each piece had to be analyzed. Hence, 
the nature of the fracture determined whether a piece should 
be analyzed or not. And, in addition to the good pieces, 
only those others whose composition it seemed desirable to 
have, were analyzed. Copper was determined electrolytically 
and the zinc obtained by difference. 

Results 

The results of this research are given in the accom- 
panying tables, and are presented graphically by means of 
curve diagrams. It was thought desirable not to present 
all the data taken, as this would be too cumbrous. 

Table I gives a complete summary of the final results. 
The first column shows the copper composition of each alloy 
obtained by analysis. In the second column are recorded the 
temperatures as taken just before pouring. The third column 
shows the freezing temperatures for the corresponding com- 
positions, taken directly from the freezing curve (Fig. i). 
In the fourth column are tabulated the differences between the 
pouring temperatures and the corresponding freezing tem- 
peratures. The next column shows the ultimate tensile 
strengths in pounds per square inch, while in the following 
column are given the ultimate strengths based upon the 
reduced areas of the broken ends. Following this, we have 
the ductilities, based on five-inch lengths on the test-pieces, 
and in the last column the good pieces are designated by 
"G" and the faulty ones by "B." 

Table II gives a list of the "good" pieces of the regular 
series. 

No work was done on heat treatment. 

The tensile strength curve is shown in Fig. 4. The 
abscissas are percentages of copper, while the ordinates are 
pounds per square inch. For comparison, the values of 



Tensile Strengths of Copper-Zinc Alloys 
Table I — Summary of tests 



13 





Pouring 


Freezing 


Differ- 
ence 


Tensile 


strength 






Percent 


tempera- 


tempera- 


Original 


Fractured 


Ductility 




copper 


ture 


ture 




section 


sections 






100 


1 160 


1080 


78 


14419 




17.2 


B 


— 


1 1 70 


1082 


88 


22618 




193 


G 


95-5 


— 


— • 




30053 




17-5 


G 


94.0 


— 


— 




25243 




17-5 


B 


90.6 


— 


— ■ 


— 


29320 


85646 


28.8 


G 


90.5 


1230? 


1050 


180 


27660 


60151 


— 


G 


903 


— • 


— 


— 


31392 


71401 


30.8 


G 


88.5 


1 140 


1040 


100 


32181 


64014 


24.8 


G 


88.2 


— 


— 


— 


29443 


85189 


28.0 


G 


87.6 


1150 


1040 


no 


30690 


68461 


24.4 


G 


86.0 


— 


— 


— 


32000 







B 


86.0 


— 




— 


28200 




12.5 


B 


85.6 


— 




— 


30890 


79100 


24.8 


G 


81.3 


II20 


1015 


105 


32293 


67047 


22.8 


B 


81.3 


■ 


— 


— 


32634 


65930 


30.8 


G 


81.2 








— 


33590 


95875 


— 


G 


80.0 





— 


— 


26137 




— 


B 


80. 1 


■ 


. 


• — ■ 


30574 




— 


G 


80.5 


1 130 


1000 


130 


30486 




— 


B 


79-7 


■ 


■ — • 


— 


30900 


57830 


24-3 


G 


79.6 


1 140 


1000 


140 


31899 


64642 


26.1 


B 


77-8 





■ — • 


— 


31199 


65000 


— 


B 


77-3 


• 


— 


— 


27560 


54687 


24. 6 


B 


77.0 


I2IO 


985 


225 


27449 


48789 


24.9 


B 


76.1 


1080 


980 


100 


32323 


51933 


29.6 


G 


76.0 





— • 




29100 




— 


B 


75-3 


1 160 


980 


180 


26311 


45145 


22.2 


B 


74-1 


1220 


970 


250 


31820 




— 


B 


74-3 


1200 


970 


230 


32000 


58300 


— 


B 


73-3 


1020 


960 


60 


33955 


65200 


— 


B 


72.3 


1090 


960 


130 


31101 


49563 


— 


G 


72.0 





' 


— 


24900 




— 


B 


71.9 


I 100 


960 


140 


34449 


64600 


31-4 


G 


70.9 


1070 


950 


120 


29138 


41800 


— 


B 


70.5 





■ — ■ 


— 


32300 




— 


B 


70.5 





— 


— ■ 


19400 


26748 


II .2 


B 


70.3 





— 


— 


26752 


45368 


— 


G 


70.2 


1 100 


950 


150 


30528 




— 


G 


70.2 


• 


— ■ 


— 


28983 




22.7 


B 


68.8 


• 


— 


— 


33090 


48500 


60.4 


B 


66.5 


1030 


920 


no 


34000 




— 


B 


66.3 


1030 


920 


no 


36465 


64262 


35-6 


G 



14 



/. M. Lohr 



Table I — {Continued) 





Pouring 


Freezing 


Differ- 
ence 


Tensile 


strength 






Percent 


tempera- 


tempera- 


Original 


Fractured 


Ductility 




copper 


ture 


ture 




section 


sections 






65.8 


1 100 


915 


185 


35200 


67500 


29.1 


G 


65 


8 


1070 


915 


155 


36701 


75000 


315 


B 


65 


2 


— 


915 





35800 




34- I 


G 


64 


5 


1020 


910 


no 


41359 


87300 


— ■ 


B 


63 


I 


1030 


900 


130 


46559 


108000 


— 


G 


62 


7 


1075 


893 


180 


47457 


82250 


30.8 


B 


62 


3 


1050 


890 


160 


47715 


120500 


36.2 


G 


62 


3 


1030 


890 


140 


50917 


86620 


31-8 iB 


62 


3 


1020 


890 


130 


52300 


89730 


34-8 


G 


61 


4 


950 


890 


60 


53043 


99509 


29.8 


G 


61 


I 


1000 


890 


no 


55555 


101800 


25.2 |G 


60 


9 


980 


890 


90 


56355 


127990 


31.6 iG 


60 


6 


1060 


890 


170 


50149 


73799 


25.2 jB 


60 


5 


940 


890 


50 


562n 


103230 


24.1 |g 


60 


3 


1000 


890 


no 


57409 


97153 


26.0 IG 


59 


8 


1080 


890 


90 


58139 


104166 


20.4 G 


59 


4 




— 


— 


55800 


135621 


38.0 !G 


59 





1000 


890 


no 


56147 


80117 


21.0 i G 


58 


I 


950 


890 


60 


62909 


81400 


— G 


57 


7 


960 


885 


75 


55971 


67000 


— G 


57 


I 


1000 


885 


115 


66910 


. 


— fG 


57 





950 


885 


65 


59454 


71509 


9.6 G 


56 


7 


1050 


885 


165 


69534 


93421 


— G 


56 


4 


1030 


885 


145 


68806 


95301 


14. 1 !g 


55 


7 


lOIO 


885 


125 


63697 




II-4 ;b 


55 


4 


1050 


885 


165 


71193 


95515 


14.8 


G 


55 





950 


885 


65 


59666 


96728 


17.0 


B 


54 


9 


1000 


880 


120 


62n9 


76504 


12.8 


G 


54 


8 


1050 


880 


170 


62555 


87643 


12.0 G 


54 


8 


950 


880 


70 


57835 


74510 


98 B 


54 


I 


1050 


880 


170 


68181 


94458 


13-6 IB 


53 





980 


880 


100 


49900 


60325 


9.2 ;g 


53 





1050 


880 


170 


66026 


81311 


— iG 


53 





1040 


880 


160 


58349 




— B 


52 





— 


— 


— 


42900 




- ;B 


48 


I 


— 


— 


— 


10080 




- B 


48 


5 


— 


— 


, 


14000 




— B 


-47 


5 


— 


— 




24531 




— 


G 



Tensile Strengths of Copper-Zinc Alloys 



15 



Table II — "Good" pieces in regular series 



X crccnt 


Pouring 


Freezing 


Differ- 


Tensile 


strength 




r*r\T\T\f^Y 


tempera- 


tempera- 


ence 


Original 


Fractured 


Ductility 


copper 


ture 


ture 




section 


sections 




100. 


1 170 


1082 


88 


22618 




193 


95-5 


— 


— 


— 


30053 




17-5 


90.6 




— 


— 


29320 




— 


90.3 




— 


— 


31392 


71401 


30.8 


88.5 


1 140 


1040 


100 


32181 


64014 


24.8 


88.2 


— 


— 


— 


29443 


85189 


28.0 


87.6 


I150 


1040 


no 


30690 


68461 


24.4 


85.6 


— 


— 


— 


30890 


79100 


24.8 


81.3 


— 


— 


— 


32634 


65930 


30.8 


81.2 


— 


— 


— 


33590 


95875 


36.8 


80. 1 


— 


— 


— 


30574 




— 


79-7 


— 


— 


— 


30900 


57830 


24' 3 


76.1 


1080 


985 


95 


32323 


57933 


29,6 


72.3 


1090 


960 


130 


31101 


49563 


— 


71.9 


1 100 


960 


140 


34449 


64600 


— 


70.2 


1 100 


950 


150 


30528 




— 


68.8 


— 




— 


33090 


48500 


60.4 


66.3 


1030 


920 


no 


36465 


64262 


35-6 


65.8 


HOG 


915 


185 


35200 


67500 


29.1 


65.2 





— 


— 


35800 




34- I 


63- 1 


1030 


900 


130 


46559 


108000 




62.3 


1020 


890 


130 


52300 


89730 


34-8 


62.3 


1050 


890 


160 


47715 


102500 


36.2 


61 .4 


950 


890 


60 


53045 


99509 


29.8 


61. 1 


1000 


890 


no 


55555 


101800 


25.2 


60.9 


980 


890 


90 


56355 


127990 


31.6 


60.5 


940 


890 


50 


562n 


103230 


24.1 


60.3 


1000 


890 


no 


57409 


97153 


26.0 


59-8 


1080 


890 


190 


58139 


104166 


20. 4 


59-4 


• 


— 




55800 


135621 


38.0 


590 


1000 


890 


no 


56147 


8on7 


21 .0 


58.1 


950 


890 


60 


62909 


81400 


— 


57-1 


1000 


885 


115 


66910 




— 


570 


980 


889 


95 


61754 


63900 


9.6 


56.7 


1050 


885 


165 


69534 


93421 


— 


56.5 


1030 


885 


145 


68806 


95301 


14.0 


55-4 


1050 


885 


165 


71193 


95515 


14.8 


54-9 


1000 


880 


120 


62119 


76504 


12.8 


54-8 


1050 


880 


170 


62555 


87643 


12.0 


530 


1050 


880 


170 


66026 


81311 


— 


47-5 





— 


— 


24531 




— 



i6 



/. M. Lohr 



Thurston and Mallet are also given on the same plate. There 
is a slight increase in the tenacity with the first addition of 
zinc, after which the values remain almost the same through- 
out the a field, increasing only about 5000 pounds per square 
inch over the range to about 66 percent copper. From that 





























bg bg 






b, 


b 


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■J 






70 


































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H 








60 
































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/ 






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50 


\ 




























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1 v 








Tl 


\ 
























,w 




r 


V 


1. ! 


p+' 


r 




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Ai 


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Sr- 


H— 


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.O)- 

c 

(D 

w 
. ffi _ 

To 

.c _ 
































1 


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dL> 














(X 














DS+P 




p 
































170- 


ik 


— 


— 


^^. 


k 


^^_. 


1^4 


— 


._. 






























=er 


cer 


T C 


3PP 


er 


















L 




u 











100 



90 



80 



70 b. 



60 



50 



Fig. 4 



point there is a very sudden increase, the values going up 
rapidly to a maximum at 55.4 percent copper. The values 
fall very gradually from that point to that of 53 percent 
copper, while a very sudden drop is noticed in the alloys 
containing from 53-47.5 percent copper. Beyond this no 
work was done, as these alloys are very brittle and not of 
very great practical use. Owing to the great number of 
castings made, values of close compositions were obtained, 
resulting in a very smooth cur\^e. 

Since the test-pieces used in this investigation were all 
quenched immediately after casting, it was predicted that the 
lines 62^., hf)^ and c^^, marking respectively the boundaries 
between the a, a -f ,/? and pure ,5 fields, would be somewhat 
changed from the positions which they occupy on the equilib- 
rium diagram (Fig. i). In order to determine the extent 



Tensile Strengths of Copper-Zinc Alloys 17 

of these changes, a series of specimens taken from the ends of 
various test-pieces were examined microscopically and photo- 
graphed. The dendritic structure of the a crystals referred 
to by Shepherd/ was seen very plainly in specimens con- 
taining 81.3, 74.6, 71.9, and 66.3 percent of copper. How- 
ever, the 65.8 percent alloy showed small areas of /? crystals 
scattered through the great mass of a crystals. This shows 
that the field of pure a ends at about 66 percent copper. 
Comparison w4th the diagram will show this position to be 
somewhat to the left of the line h.jb.^, as obtained under equilib- 
rium conditions. In a similar manner, we find the line h^h^ 
moved to the left. The 55.4 percent alloy was composed 
entirely of pure ^, while the 57.1 percent alloy showed a con- 
siderable mixture of a crystals, indicating very plainly that 
pure ,5 extends almost to 57.0 percent copper. On the other 
hand, the position of the line cfi^ was found to change some- 
what to the right of that shown on the equilibrium diagram. 
The 53.0 percent alloy consisted entirely of pure ,5, whereas 
the one containing 47.5 percent copper was shown to consist 
of about three-fourths /5, distributed through the y metal. 
This indicates that pure /? must cease to exist at about 49 or 
50 percent copper. Remembering that the castings used in 
this work were quenched at about 7oo°-8oo°, and before 
equilibrium was reached, we can account very satisfactorily 
for the new positions of these boundary lines. In the several 
figures in this paper the positions of the boundary lines of the 
different phases as found here, are contrasted with their 
positions on the equilibrium diagram. The latter are re- 
presented by dotted lines, while the heavy lines show the 
boundaries obtained in this work. 

If we compare the tensile strength curve with the posi- 
tions of the boundary lines here established, we find a very 
close relationship. Throughout the a field there is only a 
slight change in the tensile strengths. At about 66 percent 
copper, where the ^ crystals begin to appear, the strengths 



Jour. Phys. Chem., 8, 427 (1904). 



i8 



/. M. Lohr 



begin to increase, and continue to increase throughout the 
range of the metal composed of a + /? crystals. The maximum 
strength is found to lie wholly in the p field. As we ap- 
proach the ;- field the strengths fall rapidly, until at 47.5 per- 
cent copper where the amount of p is small, the tenacity is 
only about 25,000 pounds per square inch. 

Let us now compare the results of this paper with those of 
Mallet and Thurston. Mallet's strength of pure copper is 
hardly comparable here, as his test- pieces were prisms 0.25 
inch square. It will be referred to later. His results be- 
tween 90 and 75 percent copper agree well with Thurston's, 
but he seems to have neglected the section of greatest change 
in strengths, as his work includes no tests between 66 and 49 
percent copper. Thurston's curve is of the same general 
form as that obtained by the writer, but much more irregular. 
For compositions around 70 percent copper, and for those con- 
taining less than 63 percent copper his values are consider- 
ably lower. His maximum is at about 58 percent copper. 



RO 




























b 


^^ 






3, 


b, 


< 










































/ 


~^l 








70 




































n 


^ \ 








































4 


/^ 


c\\ 








60 


































f 




u 








































V 




W 


y J 


3+1 


r 


50 


T) 














^ 










. 


^ 


■-¥ 








\\ 








c 












^1 


y 








T 


^ 






1/ 








\ 








40 


R 








^ 


y 






OP 


^ 








/ 








\ 




\ 








^^ 








^ 








\ 


^r__ 


-= 




/ 












\ 




30 


' — ' 








— 




— 












j 












\ 




y 




























1 
















20 


CO 














oc 














|Q 


:^i3 






pi \ 


















































10 


























.0 


=5>5 


- 


— 


k 


h4 


^ 


— 


-- 


























■47u 


Y 






£. 




=er 


cer 


It c 


?OP 


per 

































100 



90 



50 



Fig- 5 



In Fig. 5, comparison has been made with the work of 



Tensile Strengths of Copper-Zinc Alloys 19 

Charpy on annealed brasses, and with that of the Alloys 
Research Committee^ on worked rods. As would be ex- 
pected, the tensile strengths of worked metal are greater than 
those of cast metal throughout the greater part of the series. 
This is due, of course, to the decrease in the grain size brought 
about by working the metal. On the other hand, for annealed 
brasses one would predict tensile strengths lower than those 
given by castings without heat treatment. This decrease 
in strength should result from larger crystals due to annealing. 
But Charpy 's results show greater strengths over the w^hole 
of the a field and a part of the a + /? fields. This must be 
very largely due, therefore, to the small size of the test-pieces 
which he used. These pieces were 5 mm in diameter, and 
consequently on quenching, would cool very rapidly, thereby 
reducing the grain size, and giving high tensile strengths. 
The presence of traces of other metals may also have had an 
effect in increasing the strengths. 

The small size of the test-pieces, and therefore the small 
grain size, will also probably account for the abnormally 
high value for cast copper obtained by Mallet, as the prisms 
used in his tests were 0.25 inch square. 

In connection with this it is also interesting to notice 
the very high tensile strengths, based on the reduced areas 
as shown in Table I. In the region of 60 percent copper 
these strengths are considerably over 100,000 pounds per 
square inch, in one case (alloy 59.4 percent copper) attaining 
a value of 137,000 pounds per square inch. This value is 
40 percent higher than the maximum obtained by the Alloys 
Research Committee with worked metal. As this is prac- 
tically the strength of the alloy at the time of break, it is in 
reality the breaking strength of "drawn" brass and shows 
the ultimate possibility of obtaining such values for metal 
thus worked. In view of this fact, and noting that extruded 
zinc^ with a tensile strength of 23,000 pounds per square inch. 



^ Proceedings of Mech. Engineers, Parts i and 2,31 (1897). 
^ Jour. Franklin Inst., 172, 558 (191 1). 



20 /. M. Lohr 

and electrolytic copper^ of 68,000 pounds per square inch 
have recently been obtained, some interesting possibilities 
for future high tensile strengths are suggested. 

In casting these alloys, little trouble was experienced 
in obtaining good homogeneous test pieces above 80 percent 
copper, but from 65-80 percent copper it was exceedingly 
difficult. The greatest difficulty was that of porosity. 

Dozens of castings were made, perfect in external ap- 
pearance, only to show upon breaking, a thin solid homo- 
geneous outer crust or shell, within which was an area of 
porosity, varying according to the conditions under which 
the metal was melted and poured. The melting was largely 
done under illuminating gas which, for the purpose of 
preventing oxidation of the zinc, was led through a perforated 
cover into the top of the crucible. On this account, it was 
thought that perhaps the molten metal had absorbed gases, 
which it could not force out when quenched immediately 
after casting. Therefore, experiments were made, keeping 
all other conditions the same, in which granulated charcoal, 
sodium chloride, and illuminating gas, respectively, were used 
as a protection for the melt. The gas was used in the ordinary 
manner — that of leading it into the top of the crucible. And 
in a few cases it was led through a carbon tube directly into 
the melt, and distributed through it by stirring with the 
tube carrying the gas. Under each of these conditions, 
several pieces were quenched immediately after they were 
removed from the mould; others were quenched after they 
had been allowed to remain in the air in the open mould for 
about three minutes; and still others were allowed to cool 
in the air. In almost every case the pieces allowed to cool 
in the air showed, upon breaking, good solid homogeneous 
metal, free from porosity. There were, however, a few 
instances in which slight traces of porosity could be noted 
even in these. But while the porosity was thus almost 
entirely prevented, the crystallization was allowed to take 



Bennett: Jour. Phys. Chem., i6, 294 (1912). 



Tensile Strengths of Copper-Zinc Alloys 2r 

place slowly, thus giving large crystals and a consequent 
reduction in strength. In every case the metal was porous 
in the pieces quenched at once. This was more marked in 
those pieces in which gas had been led into the melt. The 
best results were obtained in the cases in which quenching^ 
was done about three minutes after the metal was poured 
and the mould opened. Even when gas was used, solid 
homogeneous metal was obtained, when the pieces were 
quenched under these conditions. 

In every instance, when the broken ends showed porosity, 
a solid shell of metal was noticed on the outside of the piece, 
and also in many instances there was a distinct break, or 
pipe, in the center. In view of these experiments, a possible 
explanation is that the dissolved gases have time to escape 
when the metal is allowed to cool entirely in the air, or is 
allowed to remain in the air for a few minutes before quench- 
ing, whereas when the pieces are quenched at once the sudden 
cooling causes a thin shell of metal to form on the outside,, 
thus preventing the gases in the interior from escaping. 

As we pass from 65 percent copper toward a lesser copper 
content, a very different kind of metal is noted. This is the 
range of the mixture of a and /9 crystals. This was decidedl)r 
the easiest brass to cast, as almost every casting was solid 
and gave a good break. There was, however, a slight tendency 
toward the formation of holes lined with a bright yellow 
covering; but these were few in number. The fractures 
were mostly V shaped or oblique to the main axis of the 
piece. From 60-63 percent copper there was noticed quite 
a tendency to "neck.'' From 57 percent copper over the 
range of the /? field we find a very hard metal, with little 
ductility. In spite of the short time for crystal growth, the 
crystal structure was large as revealed by the ragged, ir- 
regular fractures. Below 50 percent copper the crystalline 
structure was pronounced and very well defined. 

The ductility curve is shown in Fig. 6. This rises 



22 



/. M. Lohr 



gradually with the addition of zinc and attains a maximum^ 
at about 65 percent copper. It drops very suddenly at about 
60 and then falls off gradually almost to zero at 47.5 percent 
copper. The maximum here shown differs somewhat from 
that obtained by other investigators, as both Thurston with 
castings and Charpy with annealed brasses found the maxi- 
mum ductility to be at about 70 percent copper. This change 
in the maximum is evidently due to the method of cooling 
employed in this work. Under equilibrium conditions, as 
seen from the curves of the investigators mentioned above, 





























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! 


=r 


b. 


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y 


























(.1" 


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4n, 
















Per 


-ce 


-iT 


COF 


Dp€ 


jr 






470' 


% 


-- 


-- 


-ex 


^\^ 


%- 


— 


— 


• 


00 






g 







- 


8 









7 





°3 ~ 


6 







5 










Fig. 6 

the maximum falls just within the limits of pure a. Be- 
yond that, the a + ,5 crystals would break down into a+ y 
at the lower temperatures. The introduction of r might 
possibly result in brittleness and decreased ductility, al- 
though this is not certain. If the ;- metal is distributed 
through the a in a highly agglomerated condition, it un- 
doubtedly would decrease the strength, whereas there is 



^ One 68.8 percent brass gave the remarkable elongation of 60.4 percent, 
but this could not be duplicated. 



Tensile Strengths of Copper-Zinc Alloys 23 

some question as to the effect of very finely divided ;- dis- 
tributed through the a metal. On the other hand, by the 
method of rapid cooling employed here, it is quite likely that 
only sufficient /? crystals were carried over into a to increase 
the ductility and thus to throw the maximum to about 66 
percent copper. This seems quite probable in view of the 
microscopic results previously mentioned. Here it was 
shown that /? began to appear at about 66 percent copper. 
Pure /? is very low in ductility but it appears that a mixture 
of a + ^, with a preponderance of a, gives the highest ductility, 
when cooled quickly after casting. 

The effect of the temperatures of pouring upon the 
strength of the brasses may best be noted by an inspection 
of Table II. A great majority of the "good" pieces were 
poured at temperatures somewhere between 100° and 200° 
above the liquidus. In a few cases, with the temperatures 
less than 100° above the liquidus, good castings were ob- 
tained, but generally the metal was too viscous to be handled 
easily, and to fill the mould properly. However, it was 
absolutely impossible to obtain good test-pieces with the 
pouring temperature more than 200° above the liquidus. 
In every case the castings were of good extenal appearance, 
but contained numerous black spots of porous material 
presumably copper oxide. This was more noticeable as the 
copper content increased. In many cases, those pieces cast 
from temperatures more than 200° above the liquidus showed 
less than a fourth of the strength which their compositions 
should have given. 

It was impossible to limit the pouring temperatures to a 
closer range than 100°, as it will be noticed by referring to 
Column 4 of Table II, that frequently, castings of about 
the same compositions gave practically the same strengths, 
with temperatures as much as 50° apart. 

In general, then, it may be said that brasses with the 
highest strengths can be obtained by having the temperature 
of pouring within the range of 100° C to 200° C above the 
liquidus. 



24 /. M. Lohr 

Conclusions 

The following conclusions may be drawn from the results 
of this work : 

1. A study of the tensile strengths of the cast brasses 
containing 47.5-100 percent copper has been made. 

2. The a brasses give almost a constant value for the 
tensile strengths. 

3. The maximum tensile strength occurs in the neigh- 
borhood of a 55 percent copper alloy, and its value is about 
71,000 pounds per square inch. 

4. The /? alloys give the highest tensile strengths. 

5. The maximum strength does not occur on a boundary- 
curve. 

6. The variations in the tensile strengths agree very 
closely with the constitution of the alloys, as proven by the 
microscopic study. 

7. A tensile strength of 137,000 pounds per square inch, 
as taken from the fractured ends, has been obtained. 

8. A maximum ductility of about 36 percent elongation 
has been obtained regularly. One piece, however, showed 
an elongation of 60.4 percent, but could not be duplicated. 

9. It is possible to obtain a cast brass having an ultimate 
tensile strength of 71,000 pounds per square inch, and an 
ultimate elongation of 14.8 percent; or, a brass having an 
ultimate tensile strength of over 36,000 pounds per square 
inch and an ultimate elongation of 35.6 percent. 

10. A method for continuous pouring of metal has been 
devised. 

11. The effect of temperatures of pouring has been in- 
vestigated. 

This work was suggested by Professor Bancroft, and 
has been carried out under his direction. This opportunity 
is taken to thank him most heartily for his continual kindly 
interest in the work, and for the many helpful suggestions 
offered during its progress. 

Thanks are also extended to Mr. C. A. Scharschu for 



Tensile Strengths of Copper-Zinc Alloys 25 

assistance both in the casting and in the metallographic part 
of the work, and to Mr. O. W. Boies for assistance in casting. 
And finally, thanks are extended to Professor Upton for some 
suggestions, and for the use of the testing laboratory of 
Sibley College. 

Cornell University, 
May, igi2 



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